In the past few years, microelectronic devices based on GaN have rapid development, and the research of spin electronic devices which are relevant to GaN get much attention. Especially, the research of magnetic metal GaN heterostructure is especially concerned. It is notable that the Fe3N with hexagonal structure is epitaxial to the GaN with hexagonal structure, and the lattice mismatch is only 1.8%, as shown in FIG. 1. It provides innate conditions for combining magnetic material Fe3N with semiconductor material GaN [1, 2].
According to different components, FexN material could be mainly divided to two categories: x<2; x≧2. When x<2, in such components the iron nitrides gets face-centered cubic structure, and appears paramagnetism, so we do not consider it. When x≧2, there are mainly ξ-Fe2N, ε-Fe3N and γ-Fe4N, the curie temperature of each one is 9K, 575K and 761K respectively. Fe2N doesn't appear ferromagnetism at a room temperature, so it has no much practical value in magneto electronics and device design. However, ε-Fe3N and γ-Fe4N have ferromagnetism at a room temperature, therefore wide attention is brought for using them in magnetic storage and other magnetic function devices[3, 4].
The advantage of Fe3N and Fe4N in device design is that they both have high spin polarization. The spin polarizations of transition-metal and alloys are shown in Table 1[5], and the spin polarizations of magnetic oxides are shown in Table 2[6]. Theoretical calculation indicates that spin polarizations of Fe3N and Fe4N are 0.5 and 0.7 respectively[7, 8], so both of them can serve as a injection layer of spin polarization current to be used for spin-electronics devices.
TABLE 1Spin polarizations of transition-metal and alloysMetalM (metal)NiCoFeNi80Fe20Co50Fe50Co84Fe16P (%) (spin334544485149polarizations)
TABLE 2Spin polarizations of magnetic oxidesMagnetic oxidesM (metal)CrO2Fe3O4La0.61Sr0.23MnO3P (%) (spin90 ± 3.64072polarizations)
Fe3N has a cubic structure, as shown in FIG. 1, which has been epitaxial on MgO(100) substrate by a single crystal structure, and it has brought widely attention in fields of magnetic recording and magnetic tunnel junction[3, 4]. Due to the difficulties of material growth[9, 10], the synthesis of thin samples of Fe3N and the research reports on its properties are less. The growth quality of films is generally not good[11].
At present, the growth methods of Fe3N films has dc magnetron sputtering and pulsed laser deposition. As these growth technology could not control the formation of crystal lattice and provide well growth environment, therefore Fe3N films with good crystal quality cannot be obtained. Yamaguchi et al., by using MBE technology[1] and AlN/3C—SiC serving as interposed layer, had extended c-axis oriented Fe3N films to Si(111) substrate successfully. Furthermore, Gajbhiye et al. had synthesized Fe3N—GaN core-shell structure, and studied its properties[2]. However, on the current all-purpose sapphire substrate, these methods cannot form Fe3N films on Al2O3 (0001) substrate.    [1] K. Yamaguchi, T. Yui, K. Yamaki et al, J. Crys. Growth 301, 579 (2007)    [2] N. S. Gajbhiye and S. Bhattacharyya, Nanotechnology 16, 2012 (2005)    [3] T. Takahashi, N. Takahashi, T. Nakamura et al, Solid State Sci. 6, 97 (2004)    [4] S. Kokado, N. Fujima, K. Harigaya et al, Phys. Stat. Sol. (c) 3, 3303 (2006)    [5] J. S. Moodera, JMMM, 1999, 200:248    [6] R. J. Soulou, Science 1999, 282:85    [7] K. Yamaguchi, T. Yui, K. Yamaki et al, J. Crys. Growth 301, 579 (2007)    [8] M. Sifkovits, H. Smolinski, S. Hellwig et al, J. Magn. Magn. Mater. 204 (1999)    [9] R. Dubey, A. Gupta and J. C. Pivin, Phys. Rev. B 74, 214110 (2006)    [10] S. Matar, B. Siberchicot, M. Penicaud et al, J. Phys. I France 2, 1819 (1992)    [11] S. L. Roberson, D. Finello, A. D. Banks et al, Thin Solid Films 326, 47 (1998)